The invention relates to a method for freezing or solidifying liquid sulfur or other materials that are substantially water insoluble and freeze at temperatures in the range of from about 80.degree. to about 300.degree. C.
Particularly, the invention is directed to production of sulfur particles that are free flowing and dust free. In particular, the method is directed to a process for producing sulfur in the form of pellets which are easy to handle and store. The process can be operated to produce pellets with low water content. More particularly, the process produces frozen sulfur in a form which minimizes the dust pollution arising from loading and handling dry bulk sulfur at producing plants and rail and ocean terminals.
Sulfur can be solidified in the form of pellets by means of prilling towers wherein droplets of sulfur are passed countercurrent to a stream of air for a sufficient length of time for the sulfur to solidify. Although the prilled sulfur is in a form which can be readily handled, the apparatus necessary to prill sulfur represents a substantial capital investment which makes the process unattractive for commercial installation.
Sulfur can also be frozen by contacting the sulfur with the surface of a chilled roll or by forming a layer of sulfur on a metal belt which carries the sulfur for a sufficient length of time for the sulfur to harden. The sulfur from these processes is in the form of lumps or flakes and is not readily flowable. The processes require considerable screening and crushing equipment to provide a material in a suitable particle size range.
U.S. Pat. No. 3,504,061 discloses a method for producing pelletized sulfur in which liquid sulfur is admitted to a turbulent body of water. The sulfur forms a small pellet and is reduced in temperature to a point below the freezing point of sulfur. The frozen sulfur is removed from the turbulent body of water and passed over a dewatering screen. If a dry pellet is required certain silicone materials are added to the water and the pellets dried. The silicone materials are necessary to overcome the tendency of the sulfur droplets to form with a narrow cone shaped depression which entraps water in the pellet. A substantially dry particle is usually required since it substantially reduces the heat required to remelt the material.
It is an object of the present invention to provide a method to freeze sulfur and other substantially water insoluble materials in the form of easily handled dustfree pellets. It is an object of the present invention to provide a process whereby substantially dry pellets can be produced. It is a further object of the present invention to provide a process which can produce substantially dry sulfur pellets utilizing relatively inexpensive equipment.